This invention relates in general to optical systems and more specifically to a fiber optic imaging system that produces a planar image field that is a non-uniform magnification or minification of a planar object field. Systems having this capability are useful in such fields as photography, astronomy, surveillance, and weapons control.
In conventional optical systems, converging and diverging lenses are, respectively, the basic devices for magnifying and minifying an object image. These lenses produce either a real or a virtual image that is generally a uniform, or linear, magnification or minification of the object. Any non-uniformity in such a system is usually of a minor order and therefore treated as a lens aberration.
It is well known in the fiber optics to achieve magnification and minification effects comparable to those achieved with lenses by means of a taper. The taper, however, differs from conventional optics in that it produces a real and visible image in the same plane, transmits light more efficiently, and generally is satisfied with a shorter optical path.
The taper is essentially an aligned bundle of optically transmissive fibers that generally has the shape of a truncated cone. Each of the component fibers of the taper is a filament of a material such as glass or quartz that has a high index of refraction. The diameter of each filament increases uniformly from the minor diameter end of the taper to the major diameter end. Magnification occurs because light from an element of the object field that enters the small end of a given fiber is trapped in the fiber by total internal reflection until it emerges from the large diameter entrance. In minification, light from an element of an object field enters the large diameter end of a fiber and is "funneled" down to the small diameter end. In either case, the light exiting from the fibers forms a planar image field corresponding to the planar geometry of the exit surface. Magnification over the image field is uniform since the diameters of each fiber end lying in each end surface are identical.